Loss of the cystic fibrosis transmembrane conductance regulator (CFTR) causes lung disease that is the major cause of morbidity and mortality in people with cystic fibrosis (CF). Yet despite outstanding progress in several areas of basic, translational and clinical research, we still do not know why do CF lungs become colonized with bacteria. On the basis of combined culture and serologic results, over 97% of patients with CF are infected with P. aeruginosa by the age of 3. Infection with P. aeruginosa is associated with pulmonary function decline and early mortality. Most current research on P. aeruginosa in patients with CF focuses on chronic infection. Knowledge of the mechanisms that allow the initial colonization of the CF airways is limited by the difficulty of clinical research, technical problems and ethical considerations. Although CF mice have been developed, during their limited lifespan they do not develop the airway disease typically found in humans. A major impediment to studying airway colonization with bacteria is the lack of an animal model (non-murine) that replicates the lung disease in humans with CF. We generated pigs with disruption of the CFTR gene. We decided to study pigs because their lungs are very similar to humans. If the CFTR-null pigs are colonized with P. aeruginosa or any other bacteria, it will be an extremely exiting discovery. It will provide an animal model that will allow investigators to fully describe mechanistically the pathogenesis of CF lung infections, in particular at the earliest period: the initial colonization of the CF airways. Our overarching hypothesis is that lack of CFTR will result in bacterial airway colonization in pig airways. We propose 3 specific aims. Specific Aim 1: CFTR null pigs are susceptible to bacteria and viral colonization. This aim will be critical in establishing how the CF lung and environmentally encountered microorganisms interact and lead to the CF phenotype. We will also determine whether CF pigs develop airway obstruction. Specific Aim 2: The airways of CFTR null pigs can be experimentally colonized by CF bacterial pathogens. Challenging the airways with bacteria that infect human CF lungs and with porcine respiratory bacterial pathogens will allow us to investigate the early pathogenesis of disease, elucidate the response to infection, and provide models for many future studies. Specific Aim 3: Lack of CFTR in pig results in abnormal mucociliary clearance, defective antimicrobial activity, and/or altered phagocyte function of macrophages. We will investigate if CFTR plays a role in each one of these antimicrobial mechanisms in pigs. We will investigate the ability of pig CF airways to clean bacterial-sized particles, transport thiocyanate, generate hypothiocyanite, and the acidification of phagosomes in both pig neutrophils and macrophages.